Macronucleus

The macronucleus is a type of nucleus that is found in ciliates, a group of protozoa that are noted for their complex cell structure and their unique form of reproduction. The macronucleus is one of two types of nuclei in ciliates, the other being the micronucleus.

Function

The macronucleus is involved in the control of non-reproductive cell functions, acting as the center of metabolic activity and growth. It contains multiple copies of most of the genes that the cell needs in its day-to-day life.

Structure

The macronucleus is typically larger than the micronucleus, from which it develops after sexual reproduction. It is usually elongated and may be banded, depending on the species. The macronucleus contains a large amount of DNA, which is organized into chromosomes that are not separated by a nuclear membrane.

Role in Reproduction

In the process of conjugation, the micronuclei of two ciliates merge and undergo meiosis, producing four haploid micronuclei. Three of these micronuclei disintegrate, while the remaining one undergoes mitosis to form two micronuclei. One of these micronuclei is exchanged between the two ciliates, and the exchanged micronuclei fuse with the micronuclei in their new cells to form a zygotic nucleus. This zygotic nucleus then undergoes mitosis to form two diploid micronuclei, one of which develops into a new macronucleus.

See also

• Micronucleus
• Ciliate
• Conjugation (biology)